1. Field of the Invention
The present invention relates to low-weight dent-resistant hollow structures. Particularly, the present invention concerns structures composed of outer sheets having a supporting core enclosed between the outer sheets or cover plates.
2. Background of the Invention
In structures for use in aviation and space travel, it has been conventional to utilize sheets of materials which are reinforced with fibers. Particularly, for example, fiber-reinforced plastic sheeting has been used. Generally, it is desired that such structures possess relatively thin outer walls, i.e., the walls being formed from the fiber reinforced plastic sheeting. However, such thin wall thicknesses are extremely costly to produce and are subject to denting and/or bulging stresses which are particularly harmful in use. Consequently, attempts have been made to provide structures wherein such outer cover sheets are supported by means of a foamed core or by a core composed of a sandwich structure having a honeycomb formation. In such cases, however, the supporting effect of the core is either insufficient, or, in the case of the honeycomb core, the stress resistance is only in the loading direction which is substantially at a right angle to the surface of the sandwich structure.
Thus, such cores provide inadequate protection with respect to denting failures resulting from stress from several different directions.
Such sandwich structures conventionally used also have the disadvantage in that the materials from which they are formed are often incompatible with the outer sheet material with respect to their thermal properties. For example, due to the difference in the coefficients of thermal expansion between the top or covering layer and the supporting core material, delamination and ultimate disappearance of the dent-resistant properties often occur. Moreover, it is also possible, under the conditions of use, that the core may deteriorate or release gases which can completely prohibit the use of such materials in certain cases.